Without exception, crude oils are discovered and recovered from porous rock formations beneath the earths surface. In this underground environment, the crude oil is in contact with salt water and alkaline contributing formations. The crude oil is recovered in the presence of water which leaches the more common alkaline metal salts such as sodium, magnesium, calcium and potassium present as the chloride, carbonate and sulfate. The crude oil is separated from water leaving behind emulsions comprising alkaline metal salts in the crude oil. A part of the crude oil refining process is known as desalting wherein washing with caustic and water neutralizes acidic components and salts are removed along with phenolic and naphthenic acids. The severity of this desalting operation varies the residual amount of the salts remaining in the crude oil as well as the amount of caustic and water wash used during the desalting operation. Following the desalting operation, the crude oil is normally separated in one of a sequence of steps comprising atmosphere and vacuum distillation with or without a preflash zone to separate the crude oil into a gaseous phase, naphtha, kerosene, light and heavy atmospheric gas oils and a residual fraction having an initial boiling point within the range of about 332.degree. C. (630.degree. F.) up to about 371.degree. C. (700.degree. F.). This residual portion of the crude oil comprising substantial material boiling above about 538.degree. C. (1000.degree. F.) is referred to in the industry as a topped crude, a reduced crude or simply a residual oil. This residual fraction normally comprises highest concentration of residual alkaline material not removed in the desalting operation and contributed in part by the caustic and water wash above discussed. In addition, there is present, depending on crude source, substantial levels of metal contaminants comprising vanadium, nickel, iron and copper contained as metallo-organic compounds such as porphyrins, asphaltenes, multi-ring cyclic compounds, and aliphatic organo acidic metal salts.
Contaminant metals of nickel and iron are known to contribute to gas make and coke make during cracking operations in the presence of relatively high concentrations of these metals. On the other hand, vanadium has been found to adversely affect a zeolite cracking catalyst activity when allowed to exist as a low melting point material which will flow at the temperature conditions encountered during catalyst regeneration and hydrocarbon cracking operations. The flow of such a vanadium compound causes pore plugging, catalyst particle agglomeration leading to defluidization thereof and, more importantly, causes an irreversible destruction of the zeolite crystalline structure employed in the catalyst composition. In addition, residual alkaline material also contacts acid cracking sites in a catalyst matrix thereby destroying its activity as well as destroying the zeolite pore structure and its active cracking sites.
The present invention particularly addresses the concept of voiding the deactivating effects of metal contaminants and alkaline material in a residual oil fraction prior to subjecting the feed to catalytic cracking in the presence of a crystalline zeolite containing cracking catalyst. The prior art refers to a crystalline zeolite material as a crystalline aluminosilicate which has a particular crystalline structure depending on the type of crystalline zeolite employed.